The ability of plants to slough off organs by an active separation of cells is distinctive to higher green plants. Plant physiologists describe this process as abscission.
As our agricultural production has become more intensified, the use of mechanical harvesters has become more and more important in agricultural production. Their use helps to keep the unit cost of production down to a reasonable level. Where hand labor is still used in harvesting crops, any practice that can help to increase the productivity of a man per unit of time, would be an important agricultural contribution.
This invention relates to the use of certain chemicals which have a positive and beneficial effect on the abscission process. They facilitate and make the harvesting of crops easier. This is a new and unique discovery and is highly important in the agricultural sector. To harvest fruit, as given in the examples above, whether it is done by hand or mechanically, a given amount of force (energy) must be applied by hand or mechanically to the fruit, or portion of the plant to be harvested, in order to force it to abscise, or come loose from the rest of the plant. It is recognized that when a great deal of force must be applied during the harvesting operation: (1) the amount of fruit harvested in a given time is reduced as compared with fruit which is more easily loosened and taken from the plant, (2) the fruit may be damaged or reduced in quality grade because of the amount of force which must be applied, (3) some fruit becomes unmarketable because of excessive damage to the fruit, and (4) the plant itself may be damaged and in the case of perennial plants such as vines or trees, this is highly undesirable; also, in the case of annual plants where multiple harvests are to be made, damage at the first or earlier pickings is undesirable and should be avoided.
Chemicals used to assist in loosening the fruit for the harvesting operation are sometimes called, in general terms, harvesting aid chemicals or fruit loosening chemicals. If the amount of force needed to separate a fruit from the rest of the plant can be reduced through the use of a chemical, this would be a significant contribution to agriculture and would be useful to farmers and growers. Such a chemical would allow pickers to pick the fruit easily and more quickly. In the case where mechanical harvesters are used, the amount of force which would have to be applied by the mechanical harvester could be reduced. More fruit per tree (per vine, or unit or row) could be harvested more easily and uniformly. Less damage to the fruit itself and to the rest of the plant would result if a chemical loosening agent effectively reduced the required harvest force. The quality of the fruit would increase because of less damage and possibly the yield per tree (per acre, or per unit of measure) would increase because of a more uniform and complete harvest. The compounds of this invention do help to loosen the fruit which is to be harvested while at the same time, they do not significantly damage the rest of the plant.
Various abscission agents have already been suggested, but these are frequently unsatisfactory on account of undesirable side-effects. An example of these is cycloheximide, which, in spite of an excellent abscission action in the case of the citrus fruits, has a great disadvantage in that it severely damages blossom and unripe fruit on the tree, has a pronounced defoliating action, and gives rise to considerable scarring on ripe fruit.
The process according to the invention comprises the treatment of the fruit-bearing plants or of the fruits themselves with an effective amount of a compound of the general formula I ##STR3## or with a salt of such a compound.
The symbols in formula I have the following meanings:
R.sub.1 is hydrogen, halogen, especially chlorine, a substituted or unsubstituted alkyl radical having 1 to 17 carbon atoms, C.sub.2 -C.sub.5 alkenyl, substituted or unsubstituted phenylalkyl or .alpha.-furyl; PA1 R.sub.2 is hydrogen, C.sub.1 -C.sub.17 substituted and unsubstituted alkyl, C.sub.3 -C.sub.6 cycloalkyl, substituted and unsubstituted phenyl, carboxy, carbalkoxy, carbanilido, a heterocyclic radical such as pyridyl and furyl, or a group ##STR4## wherein R.sub.1 ' has the same meanings as R.sub.1, n is an integer from 0 to 3. PA1 R.sub.1 and R.sub.2 taken together form a C.sub.3 -C.sub.12 ring, and PA1 R.sub.3 and R.sub.4 each independently represent hydrogen and substituted or unsubstituted radicals chosen from the group consisting of C.sub.1 -C.sub.12 alkyl, C.sub.2 -C.sub.5 alkenyl, alkylcarbonyl, phenylcarbonyl, N-alkylcarbamoyl, N-alkylthiocarbamoyl, N,N-dialkylcarbamoyl, phenylcarbamoyl, phenylalkyl, alkoxycarbonyl, phenoxycarbonyl, phenylalkoxycarbonyl, alkylthiocarbonyl, phenylthiocarbonyl, .alpha.-furyl and tetrahydropyranyl, C.sub.1 -C.sub.6 alkyl, alkoxy or alkylthio groups are preferred when forming part of substituted R.sub.1, R.sub.1 ', R.sub.2, R.sub.3 or R.sub.4 substituent groups. PA1 m denotes the number 0, 1 or 2, and PA1 R.sub.3 and R.sub.4 represent hydrogen or unsubstituted or substituted alkylcarbonyl, phenylcarbonyl, alkylcarbamoyl, dialkylcarbamoyl, alkoxycarbonyl, phenoxycarbonyl, alkylthiocarbonyl or phenylthiocarbonyl radicals; the alkyl, alkoxy and alkylthio radicals thereof again preferably containing from 1 to 6 carbon atoms.
The compounds of formula I are therefore oximes and dioximes, the O-substituted derivatives and salts. Substituents on the oxygen atom (R.sub.3 and R.sub.4) are, as can be seen above, preferably such radicals which are readily split off hydrolytically, aminolytically or metabolically in the plant or in the application agent (spray emulsion) with the formation of the free oxime group (R.sub.3 .dbd.R.sub.4 .dbd.H). Particularly suitable radicals for R.sub.3 and R.sub.4 are those used in synthetic chemistry as protective-groups of alcohols (acyl radicals, etc.).
Applicable substituents of substituted radicals R.sub.1, R.sub.1 ', R.sub.2, R.sub.3 and R.sub.4 are: halogen, the oxo group, alkoxy, phenoxy, dialkylamino, alkylthio, hydroxy, amino, nitro, N-pyrridylium, trialkylammonio, and the like. As previously indicated, C.sub.1 -C.sub.6 alkyl, alkoxy or alkylthio radicals are preferred for this purpose.
The compounds of formula I can be present as cis- and trans-forms.
Preferred compounds for the described field of applicaton are the dioxime derivatives of formula II ##STR5## wherein R.sub.1 and R.sub.1 ' each independently represent hydrogen, chlorine or methyl groups,
Salts of these dioximes are also suitable, both the salts of strong acids, such as the hydrohalides and the sulfates, and, if R.sub.3 and/or R.sub.4 is hydrogen, the salts of bases, such as the alkali metal salts and alkaline-earth metal salts, as well as the salts of other bivalent and trivalent metals, such as Fe, Cu, Zn, Mn, Co and Al, and also the salts of strong amines, such as ethanolamine and isopropanolamine.
Particularly preferred are glyoxime and derivatives of the glyoxime of formula III ##STR6## wherein R.sub.3 and R.sub.4 each independently represent hydrogen, alkylcarbonyl, alkylcarbamoyl and alkoxycarbonyl, each containing C.sub.1 -C.sub.6 alkyl or alkoxy substituent groups, as well as the above noted salts of glyoxime.
Particular compounds within the scope of the present invention include, for example, O-(2-Chloroethoxycarbonyl)butanone oxime, dichloroglyoxime, dimethylglyoxime, monomethylglyoxime, monochloroglyoxime. Particularly preferred compounds include glyoxime and dichloroglyoxime.
The active substances used according to the invention are in some cases known and are prepared in accordance with conventional techniques. Typical preparation procedures include, for example, the reaction of acetaldehyde and nitric acid and the reaction of resulting glyoxal with hydroxylamine, the electrolysis of nitric acid. See also, Beilstein, Volume 1, page 761 and supplements.
New active substances not hitherto described in the literature are, for example, glyoxime derivatives of the more restricted formula IV ##STR7## wherein R.sub.3 ' represents hydrogen, C.sub.1 to C.sub.14 alkyl, C.sub.3 -C.sub.6 alkenyl, phenylalkyl, N-alkylcarbamoyl, N-alkylthiocarbamoyl, N,N-dialkylcarbamoyl, N-phenylcarbamoyl, alkoxycarbanoyl, phenoxycarbonyl, alkylthiocarbonyl, or tetrahydropyranyl, and R.sub.4 ' represents C.sub.1 -C.sub.14 alkyl, C.sub.3 -C.sub.6 alkenyl, phenylalkyl, alkylcarbonyl, phenylcarbonyl, N-alkylcarbamoyl, N-alkylthiocarbamoyl, N,N-dialkylcarbamoyl, N-phenylcarbamoyl, alkoxycarbonyl, phenyloxycarbonyl, alkylthiocarbonyl, or tetrahydropyranyl. In each instance, the substituted alkyl, alkoxy or alkylthio group contains from 1 to 6 carbon atoms.
These compounds are also provided in a known manner by a process in which glyoxime or a salt thereof is treated in a solvent such as acetonitrile, acetone, ether, etc., and optionally in the presence of an acid-binding agent, e.g. triethylamine, with an agent introducing the radical R'.sub.3 or R'.sub.4. Suitable agents are, for example, acetyl chloride, phenylisocyanate, dimethylcarbamoyl chloride, methylbromide, chloroformic acid ester, chlorothioformic acid ester, benzylbromide, alkylisocyanates, alkylisothiocyanates, etc.